1. Field of the Invention
This invention relates to a nonvolatile semiconductor memory, and particularly to a nonvolatile semiconductor memory with which it is possible to execute read operation during erase operation or write operation.
2. Description of the Related Art
In a nonvolatile semiconductor memory such as a flash memory, the data write time and erase time are longer than the read time. When during write operation and erase operation of a nonvolatile semiconductor memory it is not possible to read out data, the performance of the system in which the nonvolatile semiconductor memory is mounted falls. To solve this problem, nonvolatile semiconductor memories having a plurality of banks that operate independently have been developed (for example Japanese Unexamined Patent Application Publication No. 11-86576).
In a nonvolatile semiconductor memory of this kind, during the execution of erase operation or write operation in one bank, it is possible to execute read operation in another bank (dual operation). However, with a single bank it is only possible to execute one operation at a time. By increasing the number of banks, it is possible to increase the number of memory regions that can be accessed at the same time; however, because the same sense amplifiers and write circuits are needed for each bank, when the number of banks increases, the chip size increases.
Also, triple operation, in which read operation, write operation and erase operation are executed simultaneously, cannot be executed with a 2-bank configuration. In related art, to execute triple operation, 3 or more banks have been necessary.
It is an object of the present invention to provide a nonvolatile semiconductor memory with which, while keeping any increase in chip size to a minimum, it is possible to execute read operation during the execution of erase operation or write operation.
It is another object of the invention to provide a nonvolatile semiconductor memory with which, while keeping any increase in chip size to a minimum, it is possible to execute read operation, write operation and erase operation simultaneously.